Oh yes, fungi of improbable size!
I got a whole pile of dirt cheap mushrooms from a local garden store, they are intended for a nice fall/winter decoration. However I think they make great terrain for fantasy sci-fi and pulp games, foreign planets or underground worlds can all do with a bit of mega fungi. I think there have been a few topics about game board with them on this forum the past few months in fact!
They came 6 to a box, 2 of each size, the moulds are the same for each size but they are organic enough shaped that they don't look identical. I have 6 or 7 more boxes so that's about 45 mushi's to work with!
They are very light, the inside is normal packaging foam with a harder shell, which seems to be very easy to paint. No visible mould lines or other marks on any of them, either.
I based the first 3 to test them. I used washers as the weight combines with the foam makes sure they don´t tip over. I need to get more large washers for the middle size, and more CD´s for the large ones, but those are cheap as well.